This invention relates to vehicle shock absorbers which are typically mounted between the wheels and chassis of an automobile, truck, motorcycle, etc. The invention relates to a shock absorber with damping characteristics that change depending upon the acceleration of parts of the shock absorber, most importantly, upon downward acceleration of the vehicle wheel. More specifically, it relates to the control of fluid flow for acceleration sensitivity in the shock absorber.
Hydraulic shock absorbers are universally employed in automotive vehicles. Each wheel of the vehicle is coupled to the vehicle chassis or frame by a spring so that bumps or dips in the road are not transmitted directly to the passengers or vehicle load. A spring alone, however, would still give a rough ride. Shock absorbers are therefore mounted in parallel with the springs to damp the accelerations applied to the chassis from the wheel. There is a long history of shock absorber development to obtain desired characteristics of passenger ride, comfort, handling for steering, road traction and the like.
Most shock absorbers are designed to have a certain operating characteristic or load-velocity curve which is a compromise of the characteristics desired for a variety of road conditions. The characteristics suitable for driving on relatively smooth road may, however, be inappropriate where the vehicle wheels may encounter short range bumps or dips. Such conditions are not limited to vehicles like those used on off-road terrain, but also include ordinary passenger and freight vehicles which may unexpectedly encounter chuck holes, speed bumps or foreign objects on the roadway.
Shock absorbers which respond to accelerations of a vehicle wheel are known in the art. One such method implemented in a standard cylinder piston arrangement allows dynamic adjustment of valves and orifices to control the flow of hydraulic fluid from one end of the cylinder to the other end through the piston in response to terrain defects. An acceleration sensitive mechanism in the piston assembly is described for this type of shock absorber in U.S. patent application Ser. No. 07/798,036.
Such acceleration sensitive shock absorbers have demonstrated a remarkable ability to improve the performance of vehicles equipped with such shock absorbers. For example, race cars equipped with acceleration sensitive shock absorbers regularly show decreased lap times of one or two seconds as compared with identical cars equipped with shock absorbers without acceleration sensitivity.
Even though a couple seconds reduction in lap time is very important in a race car, it is still desirable to provide additional improvement in an acceleration sensitive shock absorber. It is desirable to provide the enhanced performance with no additional parts in the shock absorber.